1. Technical Field of the Invention
The present invention relates to a method for removing sulfuric acid mist existing in a gas and to an apparatus for removing sulfuric acid mist used in such method.
Sulfuric acid mist generally generates in a process in which a wet gas is dried with concentrated sulfuric acid, or generates in a desulfurization equipment by condensation of SO3 in the exhaust gas with water, or sometimes generates in various other chemical processes.
As a so-called method for removing SOx, a washing system with a scrubber using an alkali solution or water as an adsorbing solution is well known. According to this system, removal of about 90% or more of SO2 is possible but only about 50% of SO3 can be removed.
Sulfuric acid mist causes deterioration of quality of products when contaminated in the products, inhibition of reaction when contaminated in a gas used in a chemical process, and corrosion of apparatus. In addition, a gas containing sulfuric acid mist is a cause of environmental pollution when it is exhausted. Therefore, it is desirable to remove the mist to the utmost.
2. Description of the Related Art
As methods for removing sulfuric acid mist, known methods include a method in which the mist is passed through a filter such as glass wool (JP-A-6-171907), a method in which an absorbent, such as titania or the like, having affinity to the mist (JP-A-5-200283), a method using an electrostatic precipitator and so on.
However, the trapped amount of the mist is limited in the method using a filter such as glass wool. When sulfuric acid mist containing minute particles of 1 xcexcm or less is subjected to the method, about 1 to about 2 ppm by volume of the mist passes unremoved even if a high effective filter for removing mist is used.
In the method using an absorbent described above, regeneration and repacking of the absorbent become necessary and thus the process management is complicated. On the other hand, the method using an electrostatic precipitator has a problem that the cost is expensive.
The purpose of the invention is to provide a method for removing sulfuric acid mist, which allows simple and highly effective removal of sulfuric acid mist, and an apparatus for removing sulfuric acid mist in such method.
The inventors of the present invention have studied a method for removing sulfuric acid mist in order to solve the above described problems, as a result, discovered that a method for removing sulfuric acid mist which comprises bubbling a gas containing sulfuric acid mist into an absorbing solution through a gas diffuser having pores with an average pore diameter of about 1,000 xcexcm or less, allows simple and highly effective removal of sulfuric acid mist.
That is, the present invention provides to a method for removing sulfuric acid mist which comprises bubbling a gas containing sulfuric acid mist into an absorbing solution through a gas diffuser having pores with an average pore diameter of about 1,000 xcexcm or less.
In other words, the invention enables effective washing and removal of sulfuric acid mist by passing a gas containing sulfuric acid mist in an absorbing solution in the form of minute bubbles through a gas diffuser having an average pore diameter of 1,000 xcexcm or less so that the gas-liquid contact is increased.
It is preferred, for enhancing efficiency of removing sulfuric acid mist, to use a porous material having an average pore diameter of about 500 xcexcm or less and a porosity of about 30% or more as the gas diffuser in the present invention. In addition, a bubble-cap type gas diffuser provided with a cap having pores with an average pore diameter of about 1,000 xcexcm or less can be used suitably.
An apparatus for removing sulfuric acid mist of the present invention comprises plural washing tanks containing an absorbing solution and equipped with a gas diffuser having an average pore diameter of about 1,000 xcexcm or less for bubbling a gas containing sulfuric acid mist into the absorbing solution, wherein respective washing tanks are connected such that the gas containing sulfuric acid mist passes through these washing tanks in order.
An preferable apparatus for removing sulfuric acid mist of the present invention comprises a washing tower, in which the inside is divided into plural stages by trays containing the gas diffuser at least in a part, a washing solution is poured on the trays for each stages so as to form washing tanks, an inlet of the gas containing sulfuric acid mist is provided at a lower part of the tower, and an outlet of the gas is provided at an upper part of the tower.
By this constitution, the gas containing sulfuric acid mist introduced from the lower part of the tower ascends in the tower while being washed at every stage in the form of minute bubbles, and therefore sulfuric acid mist can be removed with high efficiency.